Storing and recalling signals



1967 N. D. SMITH, JR, ETAL 3,357,001

STORING AND RECALLING SIGNALS Original Filed Dec. 7, 1961 4 Sheets-Sheet1 FIG, I MAGNETO-STRICTIVE ROD OUTPUT B I6 'I' 'l; I7 23 30 33 7 I57. 127 l [I (:MMWMHMMMM665666656 M I 24q v re B l9 2e PULSE 26 37 7 4, 40GEN.

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43 I JTJUL I 45 SIGNAL FIG. 2 SOURCE r INVENTORS n T f' 5 NOYES D.SMITH,JR.

WILLIAM L. ROEVER THEI ATTORNEY De c. s, 1967 N. D. SMITH, JR, ETAL-STORING AND RECALLING SIGNALS 4 Sheets-Sheet 2 5g H 33 I6 I5 I I 23 PIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII I8 I I A I I 58 4| 47 ss rfi 1 12p55 2544. 46 .7 M57 49 L 5 SIGNAL SOURCE INVENTORS NOYES 04 SMITH,JR. WILLIAML. ROEVER 7 '1 JMQ X/ /%%Am,-

THEIR ATTORNEY Dec. 5, 1967 N. D. SMITH, JR ETAL 3,357,001

STORING AND RECALL-INC: SIGNALS Original Filed Dec. 7, 1961 4Sheets-Sheet 5 o as 84 82 I 2; U 27 785 L 24 a7 5 W3 7 *1 PULSE 2 S12EGEN A M B 3s 4 I PULSE GEN.

SIGNALr25 SOURCE FIG 9 INVENTORSI NOYES 0. SMITH,JR. WILLIAM L. ROEVERTHEIR ATTORNEY Dec. 5, 1967 N. D. SMITH, JR. ETAL 3,357,001

STORING AND RECALLING SIGNALS I Original Filed Dec. 7, 1961 4Sheets-Sheet 4 23 80 '83 s4 500 M30 1* 'F ii L I R,

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INVENTORS NOYES D. SM|TH,JR. WILLIAM L. ROEVER THEIR ATTORNEY UnitedStates Patent 3,357,001 STORING AND RECALLING SIGNALS Noyes D. Smith,Jr., and William L. Roever, Bellaire, Tex., assignors to Shell OilCompany, New York, N.Y., a corporation of Delaware ()riginal appiicationDec. 7, 1961, Ser. No. 157,796, now Patent No. 3,320,596, dated May 16,1967. Divided and this application Sept. 24, 1965, Ser. No. 490,906

9 Claims. (Cl. 340174) ABSTRACT OF THE DISCLOSURE A method and apparatusfor storing and recalling a signal having an amplitude that varies withtime. The signal is stored in a rod of magneto-strictive material byestablishing a series of remanent stresses and polarizations along thelength of the rod. The signal is recalled by applying a short polarizingpulse to the rod and detecting the magnitude of the recalled signal.

This application is a division of our application Serial No. 157,796,filed December 7, 1961, now Patent No. 3,320,596.

This invention relates to the storage and recall of information whichincludes signal elements forming a sequence in time. More particularly,it is concerned with a method and a device for accumulating within astorage body a series of signal elements which vary in amplitude as afunction of time, sometimes called the analogue storage of informationas distinguished from digital storage,

and is further concerned with the recall of the information at will. Theinvention is applicable to computer circuitry, telephone circuitry,servo-mechanisms, data-storage systems, and the like. It may be notedthat although the invention in itself deals with the analogue storage ofinformation it may be applied as a component of or in conjunction with adigital computer or system.

It is known to store a sequence of pulses transiently in rods orelongate bodies of magneto-strictive materials for the purpose ofachieving a time-delay. (See U.S. Patents No. 2,495,740 to Labin et al.,January 31, 1950 and No. 2,846,666 to Epstein et al., August 5, 1958.)The signal is applied to the rod magnetically and creates a mechanicaldistrurbance which travels along the rod, setting up correspondingmagnetic fields at one or more points displaced from the point ofapplication; the variation in the magnetic field is detected at suchdisplaced point as a delayed signal. The mechanical disturbances aredissipated and are not, therefore, stored within the rod so as to besubject to recall at will.

It is an object of this invention to provide a memory device and amethod of storing information expressed as an amplitude which is afunction of time wherein the information can be recalled at will. Thesaid information may be a continuous function of time or may be asequence of pulses of like or different amplitudes with equal ornonequal time intervals between them.

A further object is to provide a device and a method of recalling orreading out the information after storage according to the above object.A specific object is to effect recall of the information substantiallynon-destructively, so that it may be recalled repetitively withoutre-storage thereof after read-out. An ancillary object is to effectread-out of the stored information either in the normal or reverse orderas the source signal. A further ancillary object is to effect read-outof the stored information on the same time-scale as the source signal oron a different time-scale.

In accordance with the invention use is made of an elongate body, suchas a solid or tubular rod, having the properties of being polarized bythe application of a polarizing stress, of retaining a remanentpolarization after removal of the polarizing stress, and of exhibiting acoupling between its polarization and mechanical stress and strain. Suchproperties occur in magnetostrictive materials and electrostrictivematerials. For convenience this class of materials is herein sometimesreferred to as electro-magnetostrictive materials.

In summary, according to the invention the source train of signalelements is applied as a series of mechanical stresses-if necessary,after transformation or amplification by a suitable transducer-to aninput point of an elongate,electro-magnetostrictive body, preferablyafter polarizing the said body, to produce mechanical stresses whichtravel along the length of the body as longitudinal or torsional waves,and applying a short polarizing stress to the body before the stresswave reaches the end of the body. The application of the shortpolarizing stress produces Within the body a remanent polarization inwhich the magnitude at various points along the length of the bodycorresponds to the magnitudes of the-mechanical stresses at those pointsat the instant that the short polarizing stress was applied. Hence theremanent mechanical stresses at spatially displaced points are fixed orfrozen at values which correspond to the amplitudes of successiveelements of the source signal which were applied at successive times.

The term short as used herein denotes a duration which is small inrelation to the duration of the elements of the signal. After the stresswave due to the source signal has become dissipated, the remanentpolarization will be different from that at the instant of theapplication of the short polarizing pulse but nevertheless a function ofthe stress at that instant. Corresponding to these remanentpolarizations, there are remanent mechanical strains. Thus, theinformation is stored in the material, which acts as a memory device.

According to a second feature of the invention the stored information isrecalled by propagating a mechanical stress through the body andobserving the effect of the stress during such propagation as a functionof time. This may be effected in various ways:

(1) According to one method a single, short acoustic recall pulse isinitiated in the body; as this pulse travels the length of the body itchanges the stress and, hence, the remanent polarization successivelyalong the spatially displaced points along the rod. This change inremanent polarization is observed as a function of time and theinformation is thereby recalled. In the usual case the recall pulse isapplied at or near the end of the body toward which the source wavetravelled during storage thereof; the elements of information are thenread off in the same time-sequence as in the source signal; one may,however, recall the information elements in reverse order by applyingthe recall pulse to travel along the body in the same direction as thesource signal, e.g., by applying it to the other end or the point ofapplication of the source signal.

(2) According to a second method the polarization is changedsimultaneously all along the length of the body. This generates newmechanical stresses along the body which have magnitudes correspondingto the remanent stresses and polarizations, and these new stressestravel along the body as waves in both directions. These stress Wavesare observed by a transducer at or near one end of the bodyusually atthe end remote from the point of application of the source signal toreconstitute the original information in its normal sequence; however,the waves may be observed at the other end for reversing the sequence.

The recall of information is substantially nondestructive, whereby it ispossible to interrogate the storage device repetitively and at will.

The mechanical stresses used to feed the source signal to the elongatebody and the stress used to recall the stored information may belongitudinal or torsional and may be of the same or of different forms.Because the velocity of propagation of longitudinal waves is differentfrom that for torsional waves the time-scale of the recalled signal maybe the same as, shorter, or longer than that of the source signal, Thus,the time-scale is unaltered when both the storage and recall stressesare longitudinal or when both are torsional; it is enlarged when theformer is compressional and the latter torsional, i.e., the timescale isincreased, and the recalled signal will be expanded over a longer timeperiod; and when the former is torsional and the latter compressional,the time-scale is decreased. However, it is preferred according to theinvention, whenever the storage and recall waves are of the same type,to employ torsional stresses because it leads to reduced dispersion.

The invention will be described in detail with reference to theaccompanying drawings forming a part of this specification, wherein:

FIGURE 1 is a perspective view of a rod of magnetostrictive material,showing the magnetic fields discussed in the specification;

FIGURE 2 is a diagrammatic view of one embodiment of the invention,using a solid memory rod of magnetostrictive material, wherein recall iseffected by applying a mechanical wave;

FIGURE 3 is a fragmentary detail view of a support at an intermediatesection of the memory rod;

FIGURE 4 is a perspective view of a modified form of an electrostrictivememory rod suitable for use in the embodiment of FIGURE 2;

FIGURE 5 is a diagrammatic view of a modified arrangement for recallingthe stored information, which involves changing the polarizationsimultaneously along the electrostrictive memory rod to propagate stresswaves therein;

FIGURE 6 is an elevation view of a magnetostrictive transducer appliedto one end of a memory rod;

FIGURES 7 and 8 are perspective views of rods of electrostrictivematerial, illustrating the method of 'applying circumferential andhelical polarizations, respectively;

FIGURE 9 is a diagrammatic view of another embodiment of the inventionwherein a memory rod of electrostrictive material is used, and recall issimilar to the systemof FIGURE 1;

FIGURE 10 is a sectional perspective view of a modified form of memoryrod wherein the magneto-electrostrictive material is applied as acoating;

FIGURE 11 is a perspective 'view of an electrostrictive transducerapplied to one end of a memory rod;

FIGURE 12 is a perspective view of a modified form of anelectrostrictive transducer; and

FIGURE 13 is a diagrammatic view of a further embodiment of theinvention wherein a memory rod of electrostrictive material is used andthe signal is recalled in a manner analogous to that of FIGURE 5.

As a preliminary'to a description of the invention reference is made toFIGURE 1 to explain the behaviour of electro-rnagnetostrictivematerials. The rod 10 is of magnetostrictive material, such as nickel, anickel alloy such as permalloy, or a ferrite. Ferrites are described byRobert L. Harvey in an article Ferrites and Their Properties at RadioFrequencies on pages 287-298 of vol. 9 of the Proceedings of theNational Electronic Conference, 1953, and may, for example, be amaterial having the formula NiO-Fe O containing a proportion of nickelto iron in the ratio of two to one atomic weights. If such a rod isplaced in a magnetic field, a stress and resultant strain is produced inthe material; materials exhibiting positive or negativemagneto-striction tend to expand or contract, respectively, in thedirection of magnetization. Conversely, when such a material isstrained, the magnetization changes. These materials exhibit remanencein magnetization and strain, and to every state of remanentmagnetization there is a corresponding remanent strain: if themagnetization is varied, the strain varies, and if the strain varies themagnetization varies. An axial magnetic field 11 can be applied to therod 10 by passing a DC. current I through a solenoid 12 disposedcoaxially therewith. A circumferential magnetic field 13 can be set upby passing an axial DC. current I, along the rod (or through a toroidalcoil such as is shown in FIGURE 4 at 42 when the rod has a centralbore).

Consider first that the axial magnetic field 11 is applied and reducedto zero. Thereafter the circumferential field 13 is applied and reducedto zero. Corresponding to each of these fields there will be a remanentmagnetization. The resultant of the remanent magnetizations is shown at14, which is the vector sum of the remanent axial magnetization B, andthe circumferential remanent magnetization B B,, the resultant, is ahelical field about the rod.

It is a property of magnetostrictive materials that if either acircumferential or axial field is present alone, and a torsional stressis applied to the rod, a helical field is generated. If the rod has astate of helical magnetization, then a compressional wave in the rodwill produce changes in this helical field. The amounts of the changesin the magnetic fields produced by various strains are related to themagnitudes and directions of the strains.

Let us suppose that the rod has only a remanent axial magnetization, Band that a torsional stress is applied to one end of the rod. Then, if acircumferential magnetic field is applied and both the stress and thefield are removed, there Will be a helical remanent magnetization whichis related to the magnitude of the torsional strain. Let us suppose thatthe rod has been given a uniform helical remanent magnetization B Then,if a compressive stress along the length of the rod is applied, thestate of magnetization will be changed and if a large magnetic field,either axial or circumferential, is applied and removed, the remanentmagnetization after the compressive stress has been removed will berelated to the size of the strain. These relationships are the physicalbasis for the invention.

An embodiment according to the invention is shown in FIGURE 2. There isshown a memory rod 15 of magnetostrictive material havingelectromechanical transducers 16 and 17 fixed rigidly to the ends andelectrically insulated therefrom. Transducer 16 is the signal-inputtransducer and 17 is used for applying a recall pulse. As was previouslyindicated, these transducers may be .of the axial or torsional type, andthe two transducers may be of the same type or different. In theembodiment under consideration both are torsional. In some constructionseach transducer casing is anchored against rotation in a support 18 or19; in others (FIG. 6) no anchor is used. Regardless of the transducerconstruction used, the rod is mounted for free torsional movement, e.g.,unsupported between the ends thereof. Additional supports, if any,should be arranged to reduce acoustic coupling to the rod to a minimum.Moreover, with torsional transducers, axial acoustic coupling therefromto the memory rod should be low. This can be achieved as is shown inFIGURE 3, wherein the rod 15 is supported from a base 20 by a ring 21containing a sponge-rubber bushing 22. The input circuit 23 to thetransducer 16 is connected to an amplifier 24 to which a source signalto be stored, e.g., from a source 25, is fed via'a circuit 26. It shouldbe understood that the sig-- =nal may be but is not, in general,sinusoidal, but may take any form, such as a square wave (suggested inthe drawing) including pulses which occur at equal or nonequal timeintervals. The transducer 17 has its input circuit 27 connected to apulse generator 28 which is controlled by b a triggering device,represented by a switch 29. The generator emits, when triggered, single,short pulse of sufficient strength to impose a strong torsional stressfrom the transducer to the rod 15.

The rod carries a helical winding 39 which is connected via a circuit 31anda double-throw switch 32 either to a source 33 of direct current(when the switch is in its B-positicn) or to an output amplifier 34(when the switch is in its A-position shown). The amplified signal istaken off via a circuit 35 to a load 36. When the switch is in itsB-position the solenoid is effective to create an axial magnetic field.

The rod 15 is further provided with means for creating circumferentialmagnetic field. This may be a circuit 37 connected to the ends of therod for transmitting a strong direct current pulse therethrough andconnected to a pulse generator 38, preferably through a double-throwswitch 39. This connection is established when the switch is in itsA-position. When in its B-position the circuit 37 can be connected to asource of direct current. The generator 38 is controlled by an amplifier41.

It will be understood that other means for creating a circumferentialmagnetic field may be used. For example, as is shown in FIGURE 4, therod 15a may be tubular and be provided with a toroidal winding 42 andconnected to a circuit 37a to the switch 39. The other elements attachedto the rod are omitted from FIGURE 4 for clarity but would be present aspreviously described.

A delay element of any suitable design is provided between the signalsource 25 and the amplifier 41. In the illustrative embodiment itincludes a delay rod 43, which may be constructed like the rod 15 and beof like material but of such length that a stress Wave can travel alongit before a simultaneously applied stress can travel the full length ofthe rod 15. The rod 43 of course need not be of magnetostrictivematerial. This rod is fixed to an electromechanical input transducer 44at one end and a mechanical-electrical output transducer 45 at the otherend, both being of the same type and anchored. It is evident that whenthe transducers 16 and 44 are of the same type, e.g., both torsional,the rod 43 must be shorter than the rod 15. The input circuit 46 of theinput transducer is connected to the output side or" an amplifier 47which is connected via a circuit 48 in shunt to the source signalcircuit 26, and the output circuit 49 of the transducer 45 is connectedto the amplifier 41.

in operation, initially the switch 32 is placed in its B-position,thereby passing a direct current through the solenoid 3i and polarizingthe rod 15 with axial magnetization. To store a signal the switch 39 ismoved to its A-position and the switch 32 is opened. The remanent axialmagnetization remains in the rod. The signal from the source 25 isthereafter applied simultaneously via the amplifiers 24 and 47 to thetransducers 15 and d4 of the memory rod 15 and the delay rod 43,respectively. Torsional waves progress along both of the rods, withamplitudes along the rods corresponding to the successive elements ofthe signal. The torsional wave in the delay rod reaches the transducer45 before the other wave reaches the end of thememory rod. The firstelement of the signal is amplified in the amplifier 41 to trigger the.pulse generator 38 to transmit a sharp electrical pulse of directcurrent through the memory rod via the circuit 37 This applies a shortpolarizing stress simultaneously throughout the length of the rod byimposing circumferential magnetizing field. When this pulse is ended theelements of the signal are stored along the memory rod as remanentmagnetizations and remanent strains.

When a tubular rod such as appears in FIGURE 4 is used the polarizingpulse is created by flowing the direct current through the winding 42from the circuit 37a, thereby creating a similar momentarycircumferential magnetizing field.

To recall the information, the switch 32 is moved to its A-position toconnect the solenoid 30 to the amplifier 34;

the switch 39 may be open or left in its A-position. The control device29 is actuated to trigger the pulse generator 28 and apply a sharpelectrical pulse to the transducer 17 at the end of the memory rod. Asingle torsional wave travels along the rod and influences the spatiallyseparated sections thereof in succession, producing a succession ofchanges in magnetic tield which are proportional to the remanentmagnetizations and, hence, to the amplitudes of the original signalelements. The effect of this propagated stress is observed by means ofthe solenoid 30, the induce EMF. from which is amplified in theamplifier 34. The original signal is reproduced in the circuit 35 andload 36. The store signal can be recalled in this manner as many timesas desired without destroying it.

When it is desired to clear the memory, the rod must be demagnetized.This can be accomplished in various ways, for example, by placing anoscillating field in the solenoid 30 and gradually reducing theamplitude of the field to zero, or by passing a sufiiciently largecurrent through the rod 15 to raise its temperature above the Curietemperature.

According to an alternative method of recalling the signal, thepolarization is changed along the length of the rod 15 and the resultantmechanical waves are detected. For this purpose the device may bemodified as is shown in FIGURE 5, wherein a torsional mechanicalelectrical transducer 50 replaces the electromechanical transducer 17.The output circuit 51 from this transducer is connected via a switch 52to an output amplifier 53, having an output circuit 54 connected to aload 55. The solenoid 30 is connected, as before, to a source of directcurrent 33, but the control switch 56 is, in this case, of thesinglethrow type. The pulse generator 38 is provided with a controlelement, represented by a switch 57, and the circuit from the amplifier41 is preferably provided with a switch 58. It is evident that theelements 53-57 correspond to elements 34-36, 32 and 29, respectively.Other elements are the same as in the previous embodiment.

The device of FIGURE 5 is used as previously described to store asignal. To recall a signal the switch 39 is placed in its A-position,the switch 52 is closed, the switch 56 is open, and the switch 58, whenprovided, is open. The control 57 is operated to trigger the generator38, thereby sending a short, strong pulse of direct current through thememory rod. This changes the polarization simultaneously along thelength of the rod and generates new torsional stresses at differentpoints having magnitudes corresponding to the remanent magnetizations atthose points. These stresses travel in both directions as torsional andcompressional waves. Both trains reach the transducer 50 which, however,is sensitive only to one typethe torsional waves in the embodimentdescribed. This transducer therefore generates electrical signals corresponding to the torsional waves, which are amplified at 53. Theoriginal signal (assuming that the transducer 16 was also of thetorsional type) is reproduced without change in time-scale in thecircuit 54 and load 55.

The system of FIGURE 5 can also operate without change in time-scalewhen the transducer 16 is of the compressional type and the transducer50 is sensitive only to compressional waves. However, when thetransducer 16 generates compressional waves in the storage cycle and thetransducer 50 is sensitive only to torsionalwaves the reproduced signalwill have its time-scale lengthened. Conversely, when the transducer 16generates torsional Waves and compressional waves are detected by thetransducer 50 the time-scale in the reproduced signal is reduced.

Although not illustrated, it will be understood that the input andoutput circuits can be provided with suitable circuit elements such asgating arrangements for permitting only the desired signal to betransmitted; this may be included in the amplifier units. It may befurther noted that mechanical stress waves which reach the ends of therods are reflected but eventually die out. Thus, in recording the signalit is the condition in the memory rod at the instant that the polarizingpulse is emitted by the pulse generator 38 that determines what isrecorded, and subsequent Waves do not alter the stored information.During recall, a gating arrangement in the amplifier 34 or 53 orassociated with the input or output of such amplifier prevents signalsdue to reflected waves from being included in the output. Because suchgating arrangements are well known in themselves, no description of themis included.

The time duration of the signal which can be stored in this systemdepends upon the length of the rod and the velocity of the stress wavethrough the rod; the latter, in turn, depends upon the nature of thewave. The velocity of compressional waves in a thin nickel rod is '5100meters per second, and a torsional wave is propagated with a velocity of3200 meters per second.

Because of this difference in the velocities of progagation it ispossible, as previously noted, to store the signal by one type of waveand recall it by another, e.g., in the case of FIGURE 1, record it by acompressional wave (the transducers 16, 44 and 45 being in this case ofthe compressional type) and recall it by a torsional wave (thetransducer 17 being of the torsional type). By this method the timescale of the signal is increased by the ratio of the velocity ofcompressional waves to the velocity of the torsional waves. Thisdecrease in the frequency band used by the signal is import-ant when itis desired to transmit the signal over a cable, as from a logginginstrument situated in a well some distance beneath the surface. Inother words, the device according to the invention can be mounted at atransmitting station and used for the purpose of increasing the durationof a signal, whereby the signal is less subject to attenuation and/orless costly transmission cables can be employed.

The device can also be used to decrease the duration of the signal andincrease the frequency of the source signal by storing the signal bymeans of a torsional wave and recalling it by means of a compressionalwave (the transducer 17 of FIGURE 1 being in this case of thecompressional type and the transducers 16, 44 and 45 of the torsionaltype). This arrangement would be useful in connection with electroniccomputers when the computation speed is greater than the speed at whichinformation is available in the original signal source.

In describing the methods of this invention the fidelity with which theinformation containing signal can be stored and recalled was notdiscussed in order to simplify the description of the basic operation ofstorage and recall. Two important sources of distortion are dispersionof the elastic waves and the non-linearity of the relationships betweenmechanical stress, magnetomotive force and magnetization.

Longitudinal elastic Waves traveling in a rod are dispersed, i.e., thevelocity of the waves is a function of their wavelength. The velocity ofthe short wavelengths is greater than the velocity of the longerwavelength waves and consequently a signal made up of waves of differentwavelengths becomes distorted as it propagates along the rod. Thiseifect can be minimized by keeping the wavelengths of interest muchlonger than the radius of the rod. For example, a signal of 100kilocycles per second will have a wavelength in a "nickel rod ofapproximately 5 centimeters. Thus if the radius of the rod is 1millimeter, very little dispersion will take place. Torsional waves in arod are not dispersive, i.e., the velocity is essentially independent ofthe wavelength. Hence the use of torsional waves is preferredparticularly for storing and recalling signals with a very shortwavelength.

The distortion due to nonlinearity can be minimized by modulating acarrier wave. Amplitude modulation can be used with the amplitude of thecarrier wave chosen so that amplitude variations of the signal occurabout a point on the most linear portion of the function relatingmagnetization to strain and magnetomotive force. For example a carrierwave with a frequency of 50 kilocycles per second may be modulated by asignal covering a range of frequencies up to 10 or 20 kilocycles persecond.

Frequency modulation can be used with an amplitude limiter toessentially eliminate distortion due to nonlinearity. The amplitude ischosen so as to use that portion of the function relating magnetizationto strain and magnetomotive force which produces the maximum responseand thus the best signal-to-noise ratio. For example, a central carrierwith a frequency of 500 kilocycles per second may be used with amodulating frequency of 20 kilocycles. Because such modulating anddemodulating systems are well known and would be incorporated into thesignal source 25 and the output signal amplifier 34 or 53, they are notfurther described herein.

A specific example of a transducer is a magnetostrictive transducer,which is shown in FIGURE 6 but not restrictive of the invention. Itincludes a rod 59 of magnetostrictive material which is connected to (ormay be integral with and be the end section of) the magnetostrictivememory rod 15. It may also be applied to the electrostrictive memory rodto be described with reference to FIGURES 9-13. It is mounted within asupport ring 60 by a foam rubber bushing 61 and forms the core of asolenoid 62, for creating an axial magnetic field. A circumferentialmagnetic field can be produced by passing an axial current through therod via a circuit 63. For torsional waves a source of direct current isconnected to the terminals 64, of the solenoid. This current may be lefton during operation of the transducer, or only the remanent polarizationcan be used. The input signal is applied to the terminals 66, 77, whichproduces a circumferential magnetic field and twists the rod to producetorsional stresses corresponding to the elements of the signal.

For compressional waves, the terminals 64 and 65 are used to pass adirect current and thereby produce remanent axial magnetization. Theseterminals are then connected to the signal source; the varying axialmagnetization produces compressional waves.

When used as a transducer for converting torsional waves into electricalpulses, e.g., as in the case of the transducers 45 and 50, a directcurrent is applied to the terminals 66 and 67, and the waves producemagnetic fields in the solenoid 62, the terminals 64 and 65 then actingas the output terminals. When the transducer is to be sensitive tocompressional waves, a direct current is passed through the solenoid 62through terminals 64 and 65 to produce an axial remanent magnetizationin the rod. The same terminals 64 and 65 are then used as the outputterminals (via suitable D.C. blocking elements) to detect a voltageproduced in coil 62 by the passage of a compressional wave through theportion of the rod covered by solenoid 62.

It will be understood that when the rod 59 lacks sufficient inertia itmay be restrained mechanically to improve the transmission of stressWaves into or from the rod 15. This involves matching the impedance;however, an accurate match is not essential.

Instead of using magnetostrictive material, electrostrictive materialsmay be used for the memory rod. These materials are members of the classof ferroelectric materials, and may be distinguished from piezoelectricmaterials, in that in the latter a reversal of the voltage reverses thesign of the resulting strain, whereas for the electrostrictive materialsthe strain is an even function of the applied voltage and the straindoes not reverse sign when the voltage is reversed. The three principaltypes of ferroelectric crystals that may be used are the rochelle salttype, the potassium dihydrogen phosphate type, and the barium titanatetype. These are described by Mason in the book Piezoelectric Crystalsand Their Application to Ultrasonics, 1950, (D. Van Nostrand Company,Inc.) page 1 and chapters XI and XII. Of these a ceramic composedprincipally of fused, powdered barium titanate is of particularinterest. It has a very high dielectric constant-of the order of1500-and can be permanently polarized by applying a transverse voltage,e.g., of the order of 20,000 volts per centimeter while the ceramic isabove its Curie temperature, cooling it to room temperature, andthereafter removing the voltage. Polarization of such material isdescribed by Mason in US Patent No.

2,742,614, April 17, 1956.

To apply circumferential polarization to such a ferroelectric material,parallel lined electrodes may be applied to the surface as is shown inFIGURE 7. Here the rod .68, e.g., of ceramic containing between 80 and95% barium titanate, has a plurality of this metallic electrodes 69, 70in engagement with the rod parallel to the central axis. The electrodes69 are connected to a common circuit 71 and the alternate electrodes 70to a common circuit 72. A direct current voltage from a source 73 isconnected to these circuits while the rod is heated to the Curie pointand cooled. When a torsional strain is applied to the polarized roda'helical polarization results.

However, if the rod is to respond to both torsional and compressionalstrains, it is necessary to apply helical polarization to the rod. Thisis shown in FIGURE 8, wherein the rod is engaged by thin metallicelectrodes 75, 76, which extend helically about the rod and areconnected by circuits 77, 78 to a source 79 of direct current potential.Although only one pair of electrodes is shown, a greater number may beused, as indicated in FIGURE 7, to cover substantially the entiresurface of the rod.

An embodiment of the invention employing such an electrostrictive memoryrod is shown in FIGURE 9, wherein the ferroelectric rod 80 has its endsmounted in transducers 81 and 82, the input circuits 23 and 27 of whichare connected to elements 2426 and 28 29, which are as previouslydescribed for FIGURE 1. The rod has one or more pairs of helicalelectrodes 83, 84 connected by a circuit 85 to a double-throw switch 86which, when in its A-position, connects the circuit 85 to the pulsegenerator 38. Parts 38 and 41-49 are as previously described. Thetransducers 44, 45, 81 and 82 may be either of the torsional orcompressional type, as was explained previously. When the switch is inits B-position the electrodes are connected to an output amplifier 87.The amplified output signal is taken off via a circuit 88 to a load 89.The electrodes are further connected to the poles of a switch 90 whichmay be a single-throw switch having at least the contacts indicated forthe A-position by which the electrodes can be connected to a source 91of alternating current the potential of which can be controlled.Optionally, the switch 90 is a doublethrow switch, as shown, andincludes further a B-position, in which the electrodes 83, 94 areconnected to a cource 92 of high direct current potential. When theswitch 90 is momentarily placed into its B- position, a remanant helicalpolarization is left in the rod 80. This operation, preliminary tostoring a signal, is not always necessary; however, it is desirable tohave an initial polarization to improve the sensitivity and thelinearity of the storage system. The switch 90 is in open position whilestoring a signal.

,To store a signal the switch 86 is placed in its A-position and thesignal from the source 25 is applied simultaneously to the amplifiers 24and 46 and, thence, to the transducers 81 and 44 to initiatetorsionalwaves to the memory rod 80 and delay rod 43, which may be ofthe same type as the rod 80 or of other material. The signal wavereaches the transducer 45 before reaching the end of the rod 80,triggering the pulse generator 38 and applying a strong, shortpolarizing pulse of direct current voltage across the electrodes 83, 84.This imposes a helical polarizing field simultaneously along the lengthof the rod. When this pulse is ended the elements of the signal arestored along the memory rod as remanent polarizations and remanentstrains.

To recall the information the switch 86 is moved to the B-position andthe control 29 is operated to apply a sharp torsional strain of shortduration to the end of the rod from the transducer 82. This wave travelsalong the rod, producing a succession of voltages between the electrodes83 and 84 which voltages are proportional to the remanent strains and,hence, to the amplitudes of the original signal elements. These voltagesare amplified in the amplifier 87, and the original signal is reproducedin the circuit 88 and load 89. As before, the stored signal can berecalled repetitively without destroying it.

To erase the signal from the memory rod the switch 86 is opened and theswitch 90 is placed in its A-position to connect the electrodes toalternating current potential. This is gradually diminished, therebydepolarizing the rod 80.

Although certain specific embodiments of the use of magnetostrictive andelectrostrictive rods were illustrated, it is evident that otherphysical arrangements may be used. For example, it is possible to bond athin layer of either magnetostrictive or electrostrictive material torods or wires of other materials which have different mechanicalproperties. This is shown in FIGURE 10, wherein a rod 93 of suitablestructural material, such as steel, is coated with a layer 94 ofmagnetostrictive or electrostrictive material.

Electrostrictive material may also be used in the transducers. As isshown in FIGURE 11, a memory rod 95, which may be eithermagnetostrictive or electrostrictive, is fixed at the end thereof to atorsional wave transducer comprising a plurality, e.g., six pie-shapedsectors 96 of barium titanate or the like which have remanentpolarizations in the directions tangential to the composite transducer,as indicated by the arrows. Each sector may be separately polarized orthe sectors may be cut from a slab of material having remanentpolarization and assembled in proper orientation. The flat ends of thecomposite transducer structure are provided with electrodes, e.g., bydepositing a film of metal by vaporization on the ends and connectingthe films to electrical connections 97 and 98, respectively, e.g., byone or more contact discs 99. The rod can be attached to themetal-coated end of the transducer by an adhesive, e.g., an epoxy resin.The connections 97 and 98 are connected to the input circuit e.g., 23 or46 of FIGURE 2. When the signal is applied to the electrodes each sector96 is stressed in shear parallel to the flat faces, thereby producing atorsional stress in the end of the memory rod 95. It is understood thatthe transducer may be mounted as is shown in FIGURE 6, it beingpreferred not to clamp it.

Another form 'of electrostrictive transducer, suitable for producingcompressional waves, is shown in FIGURE 12. In this embodiment thetransducer is a disc or rod 100 of electrostrictive material havingremanent polarization in the direction parallel to the central axis, asindicatedby the arrow, and similarly provided at its ends with electrode101 of any suitable type electrically connected to wires 102 and 103which form the input circuit. The transducer is connected, as before, toa memory rod'104. When the signal is applied to the wires 103 and 103longitudinal compressional waves are generated, which stress the end ofthe memory rod.

I, In connecting transducer of FIGURES 6, 11 or 12 to the end of a rod,the efficiency with which the mechanical waves are generated dependsupon the electromechanical impedance of the transducer and the manner inwhich it is coupled to the rod. The proper design of such transducers iswell known and will not be further discussed.

FIGURE 13 shows an embodiment using an electrostrictive rod from whichthe signal is recalled in a manner that is completely analogous to thatdescribed for FIG- URE 5. The device includes a ferroelectric memory rod80 and all reference numbers smaller than 93 denote parts described forFIGURE 9. It will be noted that the switch 860: is of the single-throwtype and that the amplifier 87 and associated elements are omitted; thatthe pulse generator 38 has a control element indicated by a switch 57a,for triggering it to emit a short, strong pulse; and that the pulsegenerator is connected to the amplifier 41 by a switch 58a. Thetransducer 82 of FIGURE 9 is replaced by a mechanical-electricaltransducer 50a, the output circuit 51a of which is connected via aswitch 521: to an amplifier 53a. The output of the latter is connectedvia a circuit 52a to a load 55a.

As was noted in connection with FIGURE 9, the switch is preferablyplaced momentarily in its B-position prior to storing a signal to placea remanent helical polarization into the rod, but this is not essential.The transducers may again be of the compressional or torsional types.

A signal is stored in the manner previously described for FIGURE 9, theswitches 58a and 86a being closed and switch 90 open.

To recall the signal, the switch 90 is left open, switch 52a is closed,and switch 58a is opened. The controller element 57a is operated tocause the pulse generator 38 to induce a short polarization pulse intothe rod 80 via the electrodes 83, 84. This change in polarizationgenerates trains of elastic waves which travel along the rod in bothdirections and including both torsional and compressional components.The signals propagated toward the transducer 50a are similar to theoriginal signal waves while those moving toward the transducer 81 willhave the original time-sequence revesed. When transducer 50a issensitive to torsional waves only, only these waves will be detected toreproduce in the amplifier 53a and in its output circuit 52a and load55a a train of corresponding signals. These will correspond to thetime-scale of the original signal when the transducer 81 was likewise ofthe torsioinal type. The same is true when both transducers 81 and 50aare of the compressional type. However, when the former is of thetorsional type and the latter of the compressional type, the time-scalewill be shortened, while if these types are reversed the time-scale willbe lengthened.

In discussing the methods of this invention stress has been placed onthe use of an initial helical polarization. This particular type ofpolarization is required if the information is stored using for examplecompressional waves and recovered by means of torsional waves. If only asingle type of wave is to be used for storage and recall, it is notnecessary to use any initial polarization. It may be desirable to useinitial polarization to obtain a larger eifect and thus improve thesignal-to-noise ratio of the system.

We claim as our invention:

1. The method of storing and recalling a signal having an amplitudewhich varies irregularly with time, which comprises the steps of (a)storing said signal as remanent stresses and magnetizations in anelongate body by (1) magnetically polarizing an elongate body of amagnetostrictive material;

(2) transducing said electrical signal into corresponding mechanicalmovements and applying the resulting movements as mechanical signalstresses to said polarized body;

(3) propagating corresponding acoustic signal waves along the length ofsaid polarized body; and

(4) establishing a series of remanent stresses and magnetizations alongthe length .of said body corresponding to said signal waves within thebody by applying to said body simultaneously to points along the lengththereof of a short magnetizing pulse having a magnetic vector orthogonalto the vector of said magnetic polarization during the said propagationof the signal waves; and

(b) subsequently recalling the stored signal by applying a shortmagnetizing pulse simultaneously to said points along the length of thebody, thereby initiating a series of acoustic waves within the body inaccordance with the remanent stresses, transducing said waves at a fixedpoint of said body into elec trical pulses, and reconstituting thesignal by ampliying the resulting pulses.

2. The method of storing an electrical signal having an amplitude whichvaries irregularly with time which comprises:

(a) initial y e ectric lly p larizing n l g dy of an el ros rictivemateria (b) transducing said electrical signal into correspondingmechanical movements and applying the resulting movements as mechanicalsignal stresses to said p0- la ized body;

( P pa a in corresp ding a ustic gnal waves along the length of saidpolarized body; and

(d) @Stablishing a series of remanent stresses and electricalpolarizations along the length of said body Corresponding to said signalwaves within the body by pp y to sa d bo y simu taneously t POint al thelength thereof a short electrical polarizing pulse having an electricvector orthogonal to the electric vector of the initial electricalpolarization during the propagation of the signal waves.

3. The method of storing and recalling a signal having an amplitudewhich varies irregularly with time, which comprises the steps of (a)storing said signal as remanent stresses and electrical polarizations inan elongate body by the steps defined in claim 2; and

(b) subsequently recalling the stored signal by applying a shortmechanical stress to the body and thereby propagating an acoustic recallpulse along the length of said body, detecting the changes inpolarization along the length of the body as the pulse passes successivepoints in the body, and reconstituting the signal by amplifying thedetected changes.

4. The method of storing and recalling a signal having an amplitudewhich varies irregularly with time, which comprises the steps .of

(a) .storing said signal as remanent stresses and electricalpolarizations in an elongate body by the steps defined in claim 2; and

(b) subsequently recalling the stored signal by applying a shortelectrical polarizing pulse simultaneously to said points along thelength of the body, thereby initiating a series of acoustic waves inaccordance with the remanent stresses, transducing said w es at a fixedpoint of s d y into electrica pulses, and reconstituting the signal byamplifying the resulting pulses,

5. The method of storing and recalling a signal having an amplitudewhich varies irregularly with time, which comprises the steps .of

(a) storing said signal as remanent stresses and polarizations in anelongate body by (l) applying said signal as a series of mechanicalsignal stresses to an elongate body of magnetostrictive material andpropagating corresponding acoustic signal waves along the lengththereof; and

(2) establishing a series of remanent stresses and polarizations alongthe length of said body cor responding to said signal waves within thebody by applying theretosimultaneously at diflerent points along thelength of the body a short polarizing pu s dur ng t sai p opa a n o hsig al waves;

(b) apply ng a shor recal polar P llse simu taneously to said pointsalong the l ngth of the body, thereby initiating a series of acousticrecall waves within the body in accordance with v he remanent stresses;

(c) one of said acoustic signal waves and said recall pulse beingtorsional and the other being compressional; and

(d) detecting the magnitudes of said recall waves at a fixed point ofsaid body whereby the time-scale of the detected recall waves isdifferent from that of the original signal.

6. A device for storing a signal having an amplitude which variesirregularly with time which comprises:

(a) a rod of an electro-magnetostrictive material;

(b) an input element attached at a point of the bar for creating aseries of mechanical signal stresses in said bar in response to anapplied signal having an amplitude which varies with time to generatecorresponding acoustic signal waves in said bar for propagationtherealong;

(c) means for applying to said bar simultaneously a ong the lengththereof a short polarizing pulse to establish a series of remanentstresses and polarizations allq'ng the length thereof corresponding toacoustic signal waves which occur within the bar at the instant thatsaid polarizing pulse is applied;

(d) means for recalling the signal stored in said body,

comprising 1) means for propagating a short acoustic recall Wave alongthe length of said body, including means for applying a polarizingrecall pulse simultaneously to points along the length of said body,thereby to initiate acoustic waves which propagate along the lengththereof in accordance to the remanent stresses therein; and

(2) means for sensing the magnitudes of said propagated waves at a fixedpoint in said body; and

(e) said input element and said means for sensing the magnitudes of thewaves being of difierent types, such that one interacts withcompressional waves and the other with torsional waves, whereby the timescale of the detected wave magnitudes is diiferent from that of theapplied signal.

7. Device for storing an electrical signal having an amplitude whichvaries with time, which comprises:

(a) a magnetically polarized bar of a magnetostrictive material;

(b) an electrical-mechanical transducer having the input connected tosaid signal and mechanically coupled to said bar for creating therein aseries of mechanical signal stresses corresponding to said signal;

(c) means for applying to said bar simultaneously along the lengththereof a magnetizing pulse having a vector component which isorthogonal to the vector of initial polarization of the bar, thereby toestablish a series of remanent stresses and magnetizations along thelength thereof corresponding to acoustic signal waves which occur withinthe bar at the instant that said magnetizing pulse is applied;

((1) means for recalling the signal from the bar which compriseselectrical means for applying to said bar a short recall magnetization.pulse simultaneously along the length of the bar, thereby to initiateacoustic waves which propagate along the length of the bar incorrespondence to the remanent stresses therein;

(e) a second transducer for detecting the said acoustic 6 waves at apoint of the bar; and

(f) one of said transducers being of the torsional type,

the other of the compressional type whereby the signal emitted by thesecond transducer has a timescale which is different from that of theoriginal signal.

8. Device for storing an electrical signal having an amplitude whichvaries irregularly with time, which comprises:

(a) an electrically polarized bar of an electrostrictive material;

(b) an electrical-mechanical transducer having the input connected tosaid signal and mechanically coupled to said bar for creating therein aseries of mechanical signal stresses corresponding to said signal;

(c) means for applying to said bar simultaneously along the lengththereof an electrical polarizing pulse having a vector component whichis orthogonal to the vector of initial polarization of the bar, therebyto establish a series of remanent stresses and polarizations along thelength thereof corresponding to acoustic signal waves which occur withinthe bar at the instant that said magnetizing pulse is applied;

(d) a second transducer for recalling the signal from the bar whichcomprises means for applying to said bar a short mechanical stress,thereby to propagate an acoustic recall wave along the bar;

(e) rneans electrically connected to said bar for detecting changes inpolarization of the bar as said recall wave passes successive pointsalong the bar; and

(f) one of said transducers being of the torsional type and the other ofthe compressional type, whereby the signal detected in said electricallyconnected means has a time-scale which is different from that of theoriginal signal.

9. Device for storing an electrical signal having an amplitude whichvaries irregularly with time, which comprises:

(a) an electrically polarized bar of an electrostrictive material;

(b) an electrically-mechanical transducer having the input connected tosaid signal and mechanically coupled to said bar for creating therein aseries of mechanical signal stresses corresponding to said signal;

(c) means for applying to said bar simultaneously along the lengththereof an electrical polarizing pulse having a vector component whichis orthogonal to the vector of initial polarization of the bar, therebyto establish a series of remanent stresses and polarizations along thelength thereof corresponding to acoustic signal waves which occur withinthe bar at the instant that said magnetizing pulse is applied;

(d) means for recalling the signal from the bar which compriseselectrical means for applying to said bar a short electrical recallpolarizing pulse simultaneously along the length of the bar, thereby toinitiate acoustic waves which propagate along the length of the bar incorrespondence to the remanent stresses therein;

(e) second transducer for detecting the said acoustic waves at a pointof the bar; and

(f) one of said transducers being of the torsional type and the other ofthe compressional type, whereby the signal emitted by the secondtransducer has a timescale which is dilferent from that of the originalsignal. References Cited UNITED STATES PATENTS 3,127,578 3/1964 Long340l74 3,173,131 3/1965 Perucca 340l74 FOREIGN PATENTS 873,367 7/1961Great Britain.

BERNARD KONICK, Primary Examiner.

M. S. GITTES, Assistant Examiner.

1. THE METHOD OF STORING AND RECALLING A SIGNAL HAVING AN AMPLITUDEWHICH VARIES IRREGULARLY WITH TIME, WHICH COMPRISES THE STEPS OF (A)STORING SAID SIGNAL IS REMANENT STRESSES AND MAGNETIZATIONS IN ANELONGATE BODY BY (1) MAGNETICALLY POLARIZING AN ELONGATE BODY OF AMAGNETOSTRICTIVE MATERIAL; (2) TRANSDUCING SAID ELECTRICAL SIGNAL INTOCORRESPONDING MECHANICAL MOVEMENT AND APPLYING THE RESULTING MOVEMENTSAS MECHANICAL SIGNAL STRESSES TO SAID POLARIZED BODY; (3) PROPAGATINGCORRESPONDING ACOUSTIC SIGNAL WAVES ALONG THE LENGTH OF SAID POLARIZEDBODY; AND (4) ESTABLISHING A SERIES OF REMANENT STRESSES ANDMAGNETIZATIONS ALONG THE LENGTH OF SAID BODY CORRESPONDING TO SAIDSIGNAL WAVES WITHIN THE BODY BY APPLYING TO SAID BODY SIMULTANEOUSLY TOPOINTS ALONG THE LENGTH THEREOF OF A SHORT MAGNETIZING PULSE HAVING AMAGNETIC VECTOR ORTHOGONAL TO THE VECTOR OF SAID MAGNETIC POLARIZATIONDURING THE SAID PROPAGATION OF THE SIGNAL WAVES; AND (B) SUBSEQUENTLYRECALLING THE STORED SIGNAL BY APPLYING A SHORT MAGNETIZING PULSESIMULTANEOUSLY TO SAID POINTS ALONG THE LENGTH OF THE BODY, THEREBYINITIATING A SERIES OF ACOUSTIC WAVE WITHIN THE BODY IN ACCORDANCE WITHTHE REMANENT STRESSES, TRANSDUCING SAID WAVES AT A FIXED POINT OF SAIDBODY INTO ELECTRICAL PULSES, AND RECONSTITUTING THE SIGNAL BY AMPLIFYINGTHE RESULTING PULSES.